Implantable drug pumps allow drug therapies to be administered to a patient outside of a clinical setting. Smaller amounts of the drug can therefore be administered over long periods of time. In addition, implantable infusion pumps may inject drugs into areas such as the intrathecal space surrounding the spinal cord, where a drug is much more effective. For example, when administering a drug such as morphine intravenously instead of orally, only one-third of that drug may be needed. In other words, the drug is three times as effective when administered intravenously. Morphine may generally be ten times as effective when administered epidurally as compared to intravenously. Further, such a drug may be ten times as effective when being administered intrathecally as compared to epidurally.
Because an implantable drug pump is surgically implanted, the operating life of the implanted device needs to be as long as possible. Referring now to FIG. 1, an example implantable infusion device 100 is shown. The device 100 includes a reservoir 104 holding the drug to be administered. A pump 108 pumps drug from the reservoir 104 into the patient's body. A control circuit 112 drives the pump 108 and is powered by a battery 116.
The operating life of the device 100 may be governed by factors including the amount of drug stored in the reservoir 104 and the dosage rate, the life of the battery 116, and the mechanical longevity of the pump 108. In various implementations, the reservoir 104 may be replenished with additional quantities of the drug while the device 100 remains implanted in a patient. In such implementations, the battery 116 is even more important in determining the lifetime of the device 100. Improving battery life may allow implanted devices to be replaced less often.